/**
 * struct ListNode {
 *  int val;
 *  struct ListNode *next;
 * };
 *
 * C语言声明定义全局变量请加上static，防止重复定义
 */
/**
 * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
 *
 *
 * @param head ListNode类
 * @param m int整型
 * @param n int整型
 * @return ListNode类
 */
struct ListNode* reverseBetween(struct ListNode* head, int m, int n ) {
    // write code here
    if (!head || m == n) return head;
    struct ListNode* cur = malloc(sizeof(struct ListNode));
    cur->val = -1;
    cur->next = head;
    struct ListNode* res = cur;
    for (int i = 0; i < m - 1; i++) {
        res = res->next;
    }
    struct ListNode* node = res->next;
    struct ListNode* temp;
    for (int i = 0; i < n - m; i++) {
        temp = node->next;
        node->next = temp->next;
        temp->next = res->next;
        res->next = temp;
    }
    return cur->next;
}